Re: [Boost-users] Re: Iterator adaptor interoperability

From: Kris Braun (kris_braun_at_[hidden])
Date: 2004-02-25 10:12:40

--- David Abrahams <dave_at_[hidden]> wrote:
> Need more details.  Post a reproducible test that
> fails compilation
> and I might be able to solve your problem.

Okay, here's all the code for the test:

#include <map>
#include <boost/iterator/transform_iterator.hpp>
#include <boost/iterator/indirect_iterator.hpp>

template< class Pair >
struct select_second {
    typedef typename Pair::second_type result_type;

    typename Pair::second_type& operator( )( Pair&
pair )
        { return pair.second; }
    const typename Pair::second_type& operator( )(
const Pair& pair ) const
        { return pair.second; }
};

template< class Iterator >
struct map_iterator {
    typedef boost::transform_iterator< select_second< 
        typename Iterator::value_type >, Iterator >
                            type;

    static type             Create( const Iterator&
iter )
                                { return type( iter );
}
};

template< class Iterator >
struct pointer_map_iterator {
    typedef typename map_iterator< Iterator >::type
                            inner_type;
    typedef boost::indirect_iterator< inner_type >
                            type;

    static type             Create( const Iterator&
iter )
                                { return type(
inner_type( iter ) ); }
};

typedef std::map< int, int* > MapType;
typedef pointer_map_iterator< MapType::iterator >
iterator_generator;
typedef pointer_map_iterator< MapType::const_iterator
> const_iterator_generator;
typedef iterator_generator::type iterator;
typedef const_iterator_generator::type const_iterator;

struct Foo {
    iterator begin( void )
        { return iterator_generator::Create( m.begin(
) ); }
    iterator end( void )
        { return iterator_generator::Create( m.end( )
); }
    MapType m;
};

void foo( void )
{
    Foo f;
    for( const_iterator i = f.begin( ); i != f.end( );
++i ) { }
}

When compiled with VC7.1, this produces:

src\util\test.cpp(53) : error C2440: 'initializing' :
cannot convert from 'iterator' to
boost::indirect_iterator<Iterator>'
        with
        [           
Iterator=pointer_map_iterator<std::map<int,int
*>::const_iterator>::inner_type
        ]
        No constructor could take the source type, or
constructor overload resolution was ambiguous
src\util\test.cpp(53) : error C2678: binary '!=' : no
operator found which takes a left-hand operand of type
'const_iterator' (or there is no acceptable
conversion)

Thanks,
Kris

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